1. Field of the Invention
The present invention relates to a magnetic head for perpendicular recording, a method of manufacturing the same, and a magnetic disk drive incorporating the same.
2. Description of the Related Art
The surface recording density of a magnetic disk drive has been increasing steadily, and it is estimated to reach 100 gigabits per square inch in 2003. However, the surface recording method in the current state has a problem that, when the recorded bit length decreases, it becomes extremely difficult to increase the surface recording density due to the thermal fluctuation of magnetization of a medium. In order to solve this problem, the perpendicular recording method that records magnetization signals in the direction perpendicular to the medium has been drawing wide attentions. Especially, the perpendicular recording method that uses a perpendicular recording medium having a soft magnetic backing layer as the magnetic recording medium, and that uses a single-pole magnetic head for recording has been conceived as a method of being immune to the thermal fluctuation and being capable of generating a strong recording magnetic field; and it is accordingly expected as a future magnetic recording method for super high density.
For example, CA-01 of the eighth 3M inter-mag joint conference held in San Antonio US in January 2001 reported the surface recording density of 60 gigabits per square inch in the perpendicular recording. Also, in the perpendicular recording method using the tip surface of a magnetic head, when the recording bit decreases accompanied with increase of the surface recording density, it becomes necessary to decrease the area of the tip surface of a single pole magnetic head in use for recording, which faces the magnetic recording medium. However, to decrease the area of the tip surface of the single pole magnetic head will reduce the possibly generated magnetic field strength substantially in inverse proportion to the area thereof, which will hinder a sufficient recording.
The first method of solving this problem is to increase the saturation magnetic flux density Bs of a magnetic material making up the single pole magnetic head; however, the theoretical limit of the saturation magnetic flux density Bs of a magnetic material is 3.0 tesla, which is only 1.5 times the magnetic flux density of the currently used material, and it is impossible to meet a demand for future high density. The second method of solving this is to devise the shape of a main pole. The JP-A No. 93112/2001, for example, provides a thin film to the tip surface area of the main pole of a perpendicular magnetic head, further provides a minute aperture to the thin film, and provides a tip such that a part of the main pole extends toward this aperture, thereby disclosing a method of enhancing the recording magnetic field at the tip of the main pole. And, the lecture number F5 of the technical digests of the magnetic recording conference held in August 2001 discloses that it is possible to increase the recording magnetic field strength by about 20% in the single pole magnetic head composed of a conventional main pole 101, coil 102, and subordinate pole 103, as illustrated in FIG. 1, by providing a taper part forming an angle θ to a tip surface 104 on the leading side 105 of the main pole. Further, the lecture number P46 of the same magnetic recording conference held in August 2001 discloses that it is possible to generate a magnetic field higher than the saturation magnetic flux density Bs, which is considered as the limit up to now, by providing four taper parts 203 on the tip of a main pole 204, as shown in FIG. 2, and by providing a tip 202 having a small tip surface area 201 on the top thereof.
However, these conventional proposals involve the following problems.
The method of providing a thin film to the tip surface area of the main pole of a perpendicular magnetic head, further providing a minute aperture to the thin film, and providing a tip such that a part of the main pole extends toward the aperture is capable of precisely controlling the amount of projection of the tip, which is advantageous; however, to shorten the length of the projection in order to increase the magnetic field strength permissible of being generated will increase leakage magnetic fields from the other parts than the projection, which leads to impossibility of recording with high linear recording density, and causes a problem of erasing information of adjacent tracks.
In the method of providing the tip of the main pole with the taper part only on the leading side, as shown in FIG. 1, the magnitude of reinforcing the magnetic field is insufficient. In the method of providing the taper parts on all the sides of the main pole, as shown in FIG. 2, since the expansion of magnetic field becomes very large, the gradient of recording magnetic field in the disk rotating direction is too small to write with high linear recording density; besides, the method creates a problem of erasing information of adjacent tracks.